The Voyager spacecraft are still functioning 42 years after launch, and NASA recently announced a plan to keep these intrepid space travelers functioning as they continue their journeys beyond the Solar System. However, as power on each of the two craft continues to dwindle, difficult decisions need to be made soon regarding the future of the most-traveled spacecraft ever produced by humans.
Since their launch, these two robotic explorers have returned unprecedented science, and they are still sending back data more than four decades after leaving Earth. Now, they are the first craft to journey beyond our family of planets, far exceeding their original missions.
"It’s incredible that Voyagers’ instruments have proved so hardy. We’re proud they’ve withstood the test of time. The long lifetimes of the spacecraft mean we’re dealing with scenarios we never thought we’d encounter. We will continue to explore every option we have in order to keep the Voyagers doing the best science possible,” said Voyager Project Manager Suzanne Dodd of NASA’s Jet Propulsion Laboratory.
The Long and Winding Road
Launched from Earth in 1977, this pair of spacecraft have already carried out the longest journey ever by robotic explorers in the depths of space. But, as time goes on, their power supplies are slowly dying, providing less power to the vehicles. This means engineers need to make some difficult decisions regarding which instruments and thrusters should remain active, and which should be turned off to preserve power.
Voyager 2 is in better shape than its sibling, which ironically means that NASA must make decisions regarding this craft before deciding on the fate of instruments aboard Voyager 1. With an additional instrument drawing power, energy reserves aboard Voyager 2 are draining faster than aboard its twin explorer.
In November 2018, Voyager 2 exited the heliosphere, a protective bubble of ionized particles emanating from the Sun. This region, often called the heliopause, is generally classified as the boundary to interstellar space. Voyager 1 passed that milestone in August 2012.
Cold Encounters of the Brrr Kind
One of the instruments which revealed the news that Voyager 2 reached this outer limit of the Solar System was the cosmic ray subsystem instrument (CRS). A heating unit for that detector has since been shut off, in an effort to save power for other instruments. The CRS aboard Voyager 1 failed in 1980, long before it reached the outer limits of the Solar System.
Despite frigid conditions featuring an ambient temperature of 59 degrees below zero Celsius (-74 F), the hardy CRS aboard Voyager 2 is continuing to return data to engineers on the ground. Prior to launch, this device was only tested to temperatures of -45 C (-49 F).
Since exiting the heliosphere, the Voyager spacecraft have been humanity’s first explorers beyond the Solar System. Since that time, the intrepid pair have been exploring space, measuring galactic cosmic rays and other forms of energy streaming between families of planets.
“The environment they explore is colder, subtler and more tenuous than ever before, and yet the Voyagers continue on, exploring and measuring the interstellar medium, a smorgasbord of gas, plasma and particles from stars and gas regions not originating from our system,” NASA describes.
Voyager 2 still has five active instruments, including two detectors designed to measure the plasma (ionized gases with free-flowing electrons) coming fro the Sun, and a magnetometer to measure magnetic fields.
Since the CRS provides less data about interstellar space to scientists than the charged-particle detectors, the heater to the cosmic-ray detector was shut off first.
Each of the twin spacecraft are powered by a trio of three radioisotope thermoelectric generators (RTGs), creating heat from the decay of plutonium-238. As time goes on, the amount of energy delivered by the systems decreases by about four watts per year. Today, the RTG’s are only able to produce about 60 percent of the power they delivered at launch, limiting the number of instruments that can remain active.
Engineers keep a close look at temperatures aboard the vehicles, in an effort to keep critical systems from failing at the edges of the Solar System. If fuel lines freeze, for instance, thrusters would become inoperable, and the robotic explorers would be unable to align with Earth, and communication would be lost.
These thrusters have also started to lose power, requiring engineers to activate a different set of thrusters. This system, the known as trajectory correction maneuver thrusters, were re-activated on Voyager 1 on 2017 for the first time since 1980. Those same thrusters on Voyager 2, not used since 1989, were turned back on in July 2019.
“Both Voyager probes are exploring regions never before visited, so every day is a day of discovery. Voyager is going to keep surprising us with new insights about deep space,” said Voyager Project Scientist Ed Stone of Caltech.
Message in a Bottle
“V’Ger must evolve. It’s knowledge has reached the limits of this universe and it must evolve. What it requires of it’s god, doctor, is the answer to it’s question, ‘is there nothing more?’”
- Commander Spock, Star Trek: The Motion Picture
Each of the craft carry a golden record, designed to greet any alien beings who may encounter the vehicles someday in the decent future. This time capsule, complete with a player and playing instructions, are greetings spoken in 55 languages, from the ancient language of Akkadian to Wu, a modern dialect of Chinese. Also included on the record are 90 minutes of music, including Bach, a wedding song from Peru, and Chuck Berry’s Johnny B. Goode. The cover of these albums contains playing instructions and a map, based on the positions of pulsars, showing extraterrestrials how to find our home world.
The Voyager spacecraft are both now more than 18 billion kilometers (11 billion miles) from Earth. Traveling through uncharted territory, the pair of Voyager spacecraft continue to teach us about the nature of radiation and energy in space, knowledge which will be vital to the exploration and colonization of space.
In 2024, NASA plans to launch the Interstellar Mapping and Acceleration Probe (IMAP), which will compliment and expand the volumes of science already carried out by the Voyager spacecraft.
Did you like this article? Subscribe to The Cosmic Companion Newsletter!